Apparatus and Method for Transmitting Data in a Wireless Local Area Network

1. An apparatus for transmitting data in a station of a wireless communication system, the apparatus comprising: a data queue for storing transmission data; a data processor for processing data output from the data queue; a radio frequency (RF) module for up-converting a signal output from the data processor to a frequency band of the wireless communication system and transmitting the up-converted signal as an RF signal; a scheduler for performing scheduling, wherein a stepping index decreases when a backoff time reaches ‘0’, and the data is transmitted when both the stepping index and the backoff time reach ‘0’; and a backoff stepping generator for determining an initial value of the stepping index within a range of numbers.

2. The apparatus of claim 1 , wherein the backoff stepping generator is configured to generate a random number to determine the initial value of the stepping index.

3. The apparatus of claim 1 , further comprising: a collision rate checker for checking a collision rate of an RF signal from the RF module for a time period and providing the collision rate, wherein the scheduler is configured to calculate a collision rate trend value based on at least one value of the collision rate received from the collision rate checker, and wherein the backoff stepping generator is configured to compare the collision rate trend value with a threshold value, and increase or decrease a stepping level for determining a range of the stepping index according to the comparison result.

4. The apparatus of claim 3 , wherein the collision rate trend value is calculated using equation, f avg j = ( 1 - α ) * f current j + α * f avg j - 1 wherein f j current denotes a currently recalculated collision rate, f j−1 avg denotes a previously calculated collision rate, and α denotes a value determined according to a ratio of a previous value to a current value.

5. The apparatus of claim 3 , wherein the backoff stepping generator is configured to increase a stepping level if the collision rate trend value is greater than a maximum threshold value, and decrease the stepping level if the collision rate trend value is less than a minimum threshold value.

6. The apparatus of claim 1 , wherein the scheduler is configured to decrease a value of the stepping index from the initial value by a unit value if one idle state passes by in a state where the backoff time is ‘0’.

7. A method for transmitting data in a station of a wireless communication system, the method comprising the steps of: determining a stepping index for determining whether to transmit data, and a backoff time; decreasing the backoff time; if the backoff time reaches ‘0’, determining a transmission time of the data while decreasing the stepping index; and transmitting the data if both the backoff time and the stepping index reach ‘0’.

8. The method of claim 7 , wherein an initial value of the stepping index is determined by generating a random number within a range of numbers.

9. The method of claim 7 , wherein the stepping index is determined again upon receipt of an acknowledge signal (ACK) in response to the transmitted data.

10. The method of claim 7 , further comprising the steps of: checking a collision rate of a radio frequency (RF) signal for a period of time; calculating a collision rate trend value based on a current collision rate and a previous collision rate; and comparing the collision rate trend value with a threshold value, and determining a stepping level for determining a range of the stepping index according to the comparison result.

11. The method of claim 10 , wherein a value of the stepping level is periodically updated using the checked collision rate.

12. The method of claim 10 , wherein a value of the stepping level is updated using the collision rate trend value calculated based on the checked collision rate in accordance with the following equation for a period of time, f avg j = ( 1 - α ) * f current j + α * f avg j - 1 wherein f j current denotes a currently recalculated collision rate, f j−1 avg denotes a previously calculated collision rate, and α denotes a value determined according to a ratio of a previous value to a current value.

13. The method of claim 10 , wherein the stepping level is increased if the collision ratio trend value is greater than a maximum threshold value, and the stepping level is decreased if the collision ratio trend value is less than a minimum threshold value.

14. The method of claim 10 , further comprising the step of: performing retransmission using the stepping level value and a newly generated backoff time upon failure to receive a response signal in response to the transmitted data within a time period.